Why do people dream?

Dreams are a high-level function of the human brain. Birds and mammals have similar rapid eye movement sleep as humans, but whether they dream or not is still a mystery. Dreams are confusing and have deeply influenced people's views on the universe and the soul. The pharaoh of ancient Egypt once had a dream in which seven skinny cows ate seven fat cows. The revelation he got from it was that there would be a famine in the coming year and sufficient food must be stored. Later, this dream came true. Of course, there are still a large number of dreams that cannot be verified and have been forgotten and sealed by people, and "dream interpretation" has become a metaphysics.

Psychologist Freud is a representative figure in the study of dreams and has published the famous "The Interpretation of Dreams". He said that dreams are a release of disguised desires and an unconscious way to express fantasies such as sex or aggression, which are prohibited when awake. He divided dreams into "manifest dreams" and "hidden dreams". "Manifest dreams" are dreams that people experience, and "hidden dreams" are the true meaning of dreams, that is, the repressed subconscious. Analyzing dreams is to decipher "hidden dreams" from "manifest dreams". For example, a woman dreams that she is walking along a fence by the river and her clothes are almost caught by the fence. This is an "manifest dream"; the "hidden dream" is that the woman thinks that she is of humble origin and it is difficult for her to have a good development. Freud must be familiar with this woman in order to analyze her dream. What he has to do is to help her overcome the darkness in her subconscious mind of her humble origin.

Unlike psychologists, brain scientists value data and believe in repeatable experiments. Hobson and McCarley of Harvard University proposed the "activation-synthesis" hypothesis of dreams. They believe that dreams are the process of memory or connection formation in the cerebral cortex, and these memories and connections are activated by the random discharge of acetylcholinergic neurons in the pons. Pons neurons activate multiple areas of the cerebral cortex through the thalamus, inducing familiar images or emotions. The cerebral cortex tries to synthesize fragmented and unconnected details into a reasonable whole. According to this hypothesis, dreams are some randomly pieced together memory fragments, which can explain the absurdity of most dreams and the seeming similarity with daily life, but it cannot explain why we occasionally have some affectionate and inspiring dreams.

Some people are worried about their "excessive dreaming", while others "have no dreams at night". In fact, the average person will have 4-6 dreams every night, with shorter dreams in the first half of the night and longer dreams in the second half of the night, with a total of about one or two hours of dreaming throughout the night. Those who think they have "excessive dreaming" just remember their dreams more clearly, and "no dreams" do not necessarily mean that they really do not have dreams. As long as you wake up with a clear mind and full of energy, you don't have to worry about "excessive dreaming" or "no dreams".

"The Yellow Millet Dream" is a story that is well known to Chinese people. It tells the story of Lu Sheng who dreamed that he married a wife from a prominent family, passed the imperial examination, was promoted to a higher position, had many children and grandchildren, and enjoyed all kinds of wealth and splendor. When he died at the age of 80, he suddenly woke up and found that the yellow millet rice he cooked before going to bed was not yet cooked. Why does the dream seem to last a long time? This is because there is no reference point, just like when we watch a movie, we can see the changes of the world in a few tens of minutes, while the reality is still slowly continuing with the sunrise and the setting of the moon.

"Inception" is a classic in the history of movies. The protagonist Cobb specializes in stealing information from other people's dreams and modifying other people's subconscious through "dream making". From the perspective of brain science, it is impossible to enter other people's dreams, because the number of neurons in the brain is huge and the connections are complex. Whether inserting electrodes or analyzing brain waves, it is impossible to interpret or tamper with another person's thinking, but it is possible to transform one's own dreams to a certain extent. Because in dreams, sensory information is still uploaded, but it is not as active during the day. If we hear rumbling thunder, there may be wind and rain in the dream; if the quilt slips to the ground, we may dream of being in the snow. In order to have a good night's sleep, we should create a comfortable sleeping environment and avoid adverse stimulation.

Some people wake up from a dream and cannot move their whole body, so they think it is "sleep paralysis". In fact, it is just because the nuclei in the brain that control movement "wake up" later than normal. There is no need to make a fuss. According to data, more than 50% of people have had this experience, and it is related to life stress. This symptom is usually prone to occur when life stress is too high, work and rest time is irregular, often stay up late, insomnia, and anxiety.

Sleep is a repair of body and mind, let dreams become beautiful invitations. Whether you fall asleep in a sweet dream or wake up from a nightmare, start a new day with a good feeling, then the years and life are worth looking forward to.

(The author is an associate professor at Central China Normal University and a member of the Chinese Society for Neuroscience)